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Biosphere is a global ecosystem composed of living organisms and abiotic factors from which they derive energy and nutrients. And ecosystem is defined as structural and functional unit of the biosphere comprising of living and non-living environment that interact by means of food chains and chemical cycles resulting in energy flow, biotic diversity and material cycling to form a stable, self-supporting system
11.1 Which trophic level is incorrectly defined?
a) Carnivores – secondary or tertiary consumers
b) Decomposers – microbial heterotrophs
c) Herbivores – primary consumers
d) Omnivores – molds, yeast and mushrooms
Answer
11.1 d) Omnivores
Omnivores consume both plant and animal matter .
Molds, yeasts and mushrooms are saprophytes that feed on dead and decaying matter.
11.2 The diagram below shows a food web from the sea shore
The mussel can be described as
a) Producer
b) Primary consumer
c) Secondary consumer
d) Decomposer
Answer
11.2 c) Secondary consumer
In the food web, if we observe the position of mussels with respect to other organisms, we will notice that algae is the primary producer , microscopic animals consume algae and are the primary consumers and mussels are at the next trophic level and are the secondary consumers .
11.3 The given figure best represents:
a) Grassland food chain
b) Parasitic food chain
c) Forest food chain
d) Aquatic food chain
Answer
11.3 a) Grassland food chain
This food chain consists of grass, grasshopper, frog and snake that are present in a grassland ecosystem
11.4 Consider the following statements concerning food chains:
(i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation
(ii) Removal of most of the carnivores resulted in an increased population of herbivores.
(iii) The length of the food chains is generally limited to 3 – 4 trophic levels due to energy loss
(iv) The length of the food chains may vary from 2 to 8 trophic levels
Which two of the above statements are correct?
a) (i), (iv)
b) (i), (ii)
c) (ii), (iii)
d) (iii), (iv)
Answer
11.4 c) (ii), (iii)
Removal of 80% tigers from an area resulted in greatly increased growth of vegetation - Removal of tigers results in an increase in population of herbivores (as there are no tigers to feed on the herbivores). An increase in herbivores means more number of organisms feed on the vegetation resulting in decrease in growth of vegetation.
(Thus this statement is incorrect)
Removal of most of the carnivores resulted in an increased population of herbivores - If one trophic level is removed, the population of the previous trophic level increases as there is no organism that can consume them
(Correct)
The length of the food chains is generally limited to 3 – 4 trophic levels due to energy loss - The energy keeps on decreasing in each trophic level. This decrease is due to the heat released. As a result, the number of trophic levels is limited
(Correct)
The length of the food chains may vary from 2 to 8 trophic levels - Since energy and biomass decrease as we move from one trophic level to another, generally there are no more than four trophic levels.
(Thus the statement is Incorrect)
11.5 Which of the following groups of organisms are not included in the ecological food chain?
a) Carnivores
b) Saprophytes
c) Herbivores
d) Predators
Answer
11.5 b) Saprophytes
Saprophytes feed on dead and decaying matter .
They act at every trophic level of the food chain , thus they do not belong to any particular trophic level and they are not a part of the ecological pyramid though they play an important role in the ecosystem.
